As the demand for diesel boiling range fuel increases worldwide there is increasing interest in sources other than crude oil for producing diesel boiling range fuel and diesel boiling range fuel blending components. One such renewable source is what has been termed biorenewable sources. These renewable sources include, but are not limited to, plant oils such as corn, rapeseed, canola, soybean and algal oils, animal fats such as inedible tallow, fish oils and various waste streams such as yellow and brown greases and sewage sludge. The common feature of these sources is that they are composed of glycerides and Free Fatty Acids (FFA). Both of these classes of compounds contain aliphatic carbon chains having from about 8 to about 24 carbon atoms. The aliphatic carbon chains in the glycerides or FFAs can be fully saturated, or mono, di or poly-unsaturated.
There are reports in the art disclosing the production of hydrocarbons from oils. For example, U.S. Pat. No. 4,300,009 discloses the use of crystalline aluminosilicate zeolites to convert plant oils such as corn oil to hydrocarbons such as gasoline and chemicals such as para-xylene. U.S. Pat. No. 4,992,605 discloses the production of hydrocarbon products in the diesel boiling range by hydroprocessing vegetable oils such as canola or sunflower oil. Finally, US 2004/0230085 A1 discloses a process for treating a hydrocarbon component of biological origin by hydrodeoxygenation followed by isomerization.
Applicants have developed a process which comprises one or more steps to hydrogenate and deoxygenate (via catalytic decarboxylation, decarbonylation and/or hydrodeoxygenation) and isomerize the feedstock. The performance of the isomerization catalyst is improved by removing at least carbon dioxide from the feed to the isomerization zone. The presence of carbon dioxide or other carbon oxides may result in the deactivation of the isomerization catalyst. The carbon dioxide is removed using a hot high pressure hydrogen stripper. The effluent from the isomerization zone is separated into at least a vapor portion and a liquid portion. The vapor portion is treated using an amine absorber solution to remove at least the carbon dioxide and optionally the hydrogen sulfide so that the remaining hydrogen can be recycled back to the first reaction zone. The separated carbon dioxide and the separated hydrogen sulfide may be used for other purposes.